Control strategies of the elbow antagonist muscle pair during two types of increasing isometric contractions.

The purpose of this study was to determine if differences exist between the control strategies of the elbow flexor and extensor muscles performing stepwise and linearly increasing isometric contractions, and to determine their control strategy when active as antagonists to each other. The electromyogram (EMG) from the biceps brachii and triceps brachii were recorded during stepwise and linearly increasing contractions in flexion and extension. The power density spectrum of the EMG was determined and the median frequency (MF) for each spectrum was calculated for assessment of changes in the average conduction velocity, which reflects motor unit recruitment and derecruitment, and thereby the control strategy of the muscle. The results suggest that differences exist in the control strategies employed by a single muscle during stepwise and linearly increasing contractions. Furthermore, the antagonist triceps recruits motor units up to a higher force level during stepwise contractions than during linearly increasing contractions. The antagonist biceps derecruits motor units up to a higher force level during linearly increasing contractions than during stepwise contractions.